An ultrasonic receiver can be used to determine the location of items that contain ultrasonic emitters, such as a mobile device present within a retail, factory, or warehouse environment, for example. The ultrasonic emitter can transmit ultrasonic energy in a short burst which can be received by an ultrasonic transducer (microphone) in the ultrasonic receiver, thereby establishing the presence of the device within the environment.
Further, the use of several ultrasonic microphones distributed within the environment can also be used to provide a specific location of a particular device using techniques known in the art such as triangulation, trilateration, and the like. However, unlike radio frequency locationing systems, ultrasonic locationing systems suffer from particular problems related to the characteristics of ultrasonic sound waves and their environment of use. Firstly, ultrasonic waves are typically subject to acoustic reverberation due to multipath reflections. Therefore, a signal sent by an emitter can be interfered with by its own reverberations. Secondly, ultrasonic signals are easily subject to noise.
A solution to this problem is to provide a very short burst width of an ultrasonic signal from the emitter such that a signal sent by any emitter in the system will be properly received by the receiver before any multipath energy is included in the signal. In addition, a narrow bandwidth (high Q) receiver can be used to reject nearby environmental acoustic noise while being able to receive the very short burst. However, a high Q receiver implies a slow amplifier response time resulting in poor correlation margin between the peak output (indicating the correct TDOA) and adjacent cycles. This poor correlation margin results in a high likelihood of incorrect TDOA information which would make a receiver design with microphone spacing of less than one foot infeasible.
Accordingly, there is a need for an improved technique to resolve the above issues with ultrasonic locationing.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.